I find that a great opening scene can really set the mood for what's ahead in a movie but these ones I find the most memorable :

Zombieland

You've got a fantastic heavy metal song playing (For Whom The Bell Tolls) as these extremely well-filmed slow motion shots of zombie apocalyptic chaos keep on rolling. The dark humor (businessman running away from a zombie stripper) and the Scarface reference (man in the tuxedo shooting the machine gun) definitely made me smile.


A Clockwork Orange

Alex DeLarge's creepy stare into the camera along with the brilliant 1970s synthesizer score are great at setting off the atmosphere. Seeing the characters dressed up the way they are with the nude mannequins really add to the bizarre feel as well.


Se7en

Seeing the credits roll as the montage of a killer's journal is creepy enough by itself. The grainy film, strange handwriting and unsettling image really went well together.


I'll probably name a few more later on but I'm wondering what some of my furry friends' opinions are on this. Don't be shy to comment! : )

EDIT

The Thing

This opening immediately makes you wonder what the hell, or why the hell this is going on. Watching a helicopter chasing a dog in Antarctica with a passenger frantically trying to shoot it with a machine gun completely sucks you into the action and the plot. Ennio Morricone gave a fantastic horror film score with the bass guitar used prominently.